1. Field of the Invention
The present invention relates to the power factor which loads present to AC power lines generally and more specifically to the reduction of the harmonic currents generated on an AC power line by a DC power supply.
2. Description of the Prior Art
The power factor that a load presents to an AC power line has long been of concern. At one time, the primary concern was the inductive component of some loads. Consider, for example, the section taken from the text entitled American Electricians' Handbook (8th ed. 1961) which was edited by Terrell Croft, revised by Clifford C. Carr, and published by McGraw Hill Inc.
"143. Correction of Low Power Factor. In industrial plants, excessively low power factor is usually due to underloaded induction motors because the power factor of motors is much less at partial loads than at full load. Where motors are underloaded new motors of small capacity should be substituted. Power factor can be corrected (1) by installing synchronous motors (2) by connecting static capacitors across the line." (end of section) PA1 "(a) condition that causes a function f(x) of period 2(pi) to have only odd harmonics in its Fourier expansion is f(x)=-f(x+pi)." PA1 "6.2.7 Harmonic current. The operation of equipment shall be designed to have minimum harmonic distortion effect on the electrical system. The operation of such equipment with the following specified ratings shall not cause harmonic line currents to be generated that are greater than 3 percent of the unit's full load fundamental current between the 2nd and 32nd harmonic. . . ." PA1 "Additionally, currents with frequencies from the 32nd harmonic through 20 kilohertz (kHz) shall not exceed 100/n percent . . ." PA1 "(t)he resonant frequency of the LC circuit is chosen to reduce overvoltage peaks and improve the current phase angle. Usually the frequency is the fifth but maybe the ninth or thirteenth harmonic of the mains frequency." PA1 "(t)o reduce the third and fifth harmonic waves due to capacitor charge improving power factor . . . ." PA1 "the power factor can be improved by a large margin to 90%, as compared to 64% when the filter of this invention is not inserted." PA1 "harmonic components generated due to the distortion of the waveform at the time of charging voltage rise are suppressed by the circuits 16-20 set to have high impedance against the frequency. When the interval of the resonance frequency of the resonance circuit is set as narrow as possible to increase the frequency, its effect can be increased." PA1 ". . . the existence of harmonics in the line makes it not only impractical, but also impossible to filter out all of the harmonic current. An attempt to do so may result in overloading the filters. Accordingly, it has been determined that the better approach is to remove only a percentage of the harmonic currents generated as a result of the load and control device. Thus, a certain amount of harmonic current is reflected back into the supply line. The amount of harmonic current so reflected can be adjusted depending upon the requirements of the utility system supplying power." PA1 "(i)f the utility requirements on harmonics are more severe, it is possible to remove an even higher percentage such as 75%."
Of late, the "power factor" presented by DC power supplies has become a concern. Typically, DC power supplies employ a bridge rectifier, a filter capacitor, and, sometimes, a filter choke. The input of the rectifier is coupled (by a fuse, switch, etc.) across an AC power line. The output of the rectifier is either coupled by the choke across the capacitor (choke input filter) or, absent the choke, directly connected across the capacitor (capacitor-input filter) to develop a DC (output) potential across the capacitor.
With the choke (input filter), DC power supplies draw from the AC power line a current the waveform of which approximates a square wave (when the inductance of the choke is much greater than what is commonly referred to as the "critical" inductance). Absent the choke, the waveform more approximates a series of pulses each of which is synchronized with a corresponding peak of the AC power-line potential. In either case, the current drawn from the AC power line includes harmonic components (currents), one for each of the odd harmonics of the AC power-line frequency.
The level of the harmonic currents generated on both a three-phase and a single-phase AC power power line by both a choke-input and a capacitor-input, full-wave, DC power supply were calculated. The DC power supply was directly connected to the AC power line; and, a load resistor was directly connected across the DC power supply filter capacitor. (Small resistors were included in series with various components to facilitate the calculations.) The calculations were performed by a computer program entitled Micro-Cap II by Spectrum Software. An rms AC power line potential of 120 volts was used.
______________________________________ Harmonic currents generated on an three-phase AC power line by a choke-input, full-wave, DC power supply level of the harmonic currents relative the fundamental ______________________________________ 1st 100.0% 2nd 0.0% 3rd 0.2% 4th 0.0% 5th 19.8% 6th 0.0% 7th 14.4% 8th 0.0% 9th 0.2% 10th 0.0% 11th 8.9% 12th 0.0% 13th 7.8% 14th 0.0% 15th 0.2% 16th 0.0% 17th 5.7% 18th 0.0% 19th 5.3% 20th 0.0% 21st 0.3% 22nd 0.0% 23rd 4.2% 24th 0.0% 25th 4.1% 26th 0.0% 27th 0.3% 28th 0.0% 29th 3.3% ______________________________________ Total Harmonic Load Power Frequency Output Level ______________________________________ 2000 Watt 2000 W 60 Hz 158 V DC 30.0% ______________________________________
______________________________________ Harmonic currents generated on an three-phase AC power line by a capacitor-input, full-wave, DC power supply level of the harmonic currents relative the fundamental ______________________________________ 1st 100.0% 2nd 0.0% 3rd 0.1% 4th 0.0% 5th 62.7% 6th 0.0% 7th 36.0% 8th 0.0% 9th 0.0% 10th 0.0% 11th 3.7% 12th 0.0% 13th 8.6% 14th 0.0% 15th 0.1% 16th 0.0% 17th 2.9% 18th 0.0% 19th 1.9% 20th 0.0% 21st 0.0% 22nd 0.0% 23rd 2.8% 24th 0.0% 25th 0.7% 26th 0.0% 27th 0.0% 28th 0.0% 29th 2.0% ______________________________________ Total Harmonic Load Power Frequency Output Level ______________________________________ 2000 Watt 2000 W 60 Hz 153 V DC 73.1% ______________________________________
______________________________________ Harmonic currents generated on a single-phase AC power line by a capacitor-input, full-wave, DC power supply level of the harmonic currents relative the fundamental ______________________________________ 1st 100.0% 2nd 0.0% 3rd 94.9% 4th 0.0% 5th 85.2% 6th 0.0% 7th 72.1% 8th 0.0% 9th 56.9% 10th 0.0% 11th 41.3% 12th 0.0% 13th 26.8% 14th 0.0% 15th 15.2% 16th 0.0% 17th 8.7% 18th 0.0% 19th 8.7% 20th 0.0% 21st 10.1% 22nd 0.0% 23rd 10.0% 24th 0.0% 25th 8.3% 26th 0.0% 27th 5.7% 28th 0.0% 29th 3.4% 30th 0.0% 31st 3.0% 32nd 0.0% 33rd 3.7% 34th 0.0% 35th 4.1% 36th 0.0% 37th 3.8% 38th 0.0% 39th 2.8% 40th 0.0% 41st 1.7% 42nd 0.0% 43rd 1.3% 44th 0.0% 45th 1.7% 46th 0.0% 47th 2.0% 48th 0.0% 49th 2.0% 50th 0.0% ______________________________________ Power Factor ______________________________________ 0.42 ______________________________________ Total Harmonic Load Power Frequency Output Level ______________________________________ 200 Ohms 131 W 60 Hz 162 V DC 167% ______________________________________
It is important to note that a DC power supply employing a full wave rectifier (such as a bridge rectifier) (with properly balanced transformer, if employed, and rectifier diodes) generates harmonic currents only at the ODD harmonics of the AC power line frequency. (See, for example, the fifth, 1968, edition of Howard W. Sams & Co., Inc. (ITT) Reference Data For Radio Engineers section 42-8 "Odd or Even Harmonics," where it is stated that:
(Even if the transformer, if employed, and the rectifier diodes are not properly balanced, the level of the currents at even harmonics of the AC power line frequency will, normally, be negligible.)
DC power supplies do not conform to all of the old power factor conventions. (For example, it makes little sense to define the power factor a DC power supply presents to an AC power line as the cosine of the phase angle between the voltage developed across the input of the DC power supply and the current flowing into it.) However, they (DC power supplies) do present many of the same problems. DC power supplies, like other loads having a relatively low power factor, draw from the AC power line a current the rms level of which is disproportionately high in relation to the current that should be drawn for the power consumed. (In other words, they do conform to the definition which states that the power factor of a load (in this case, a DC power supply) is given by the ratio of the actual power consumed (in this case by a load connected to the output of the DC power supply) (as indicated by a wattmeter) to the apparent power (as indicated by the combination of a (true rms, iron-vane or thermocouple-type) ammeter and a voltmeter) (connected to the input of the DC power supply).
A relatively high AC power-line rms current is of concern in that the AC power-generating facilities and AC power-transmission facilities (lines and transformers) must be sized to accommodate the current. Further, generation and transmission losses are primarily resistive losses which, therefore, increase as the square of the level of the rms AC power-line current. It is important to note that even relatively small loads (DC power supplies) may be of concern. Although a small personal computer, for example, may not draw the level of the current drawn by a large smoke stack scrubber, if the DC power supply of the computer has a relatively low power factor, the current drawn by the DC power supply may be of such a level as to limit what may also be plugged into a single AC power-line wall outlet.
In addition, DC power supplies present many special problems, particularly for the military. As the number of airborne and shipborne systems employing DC power supplies has increased, so has the level of harmonic currents generated on the various AC power lines. With the increased levels of harmonic currents has come an increase in the above mentioned generation and transmission problems. In addition, and of potentially much more serious consequence, the high levels of harmonic currents are causing problems of undesired system interaction. As a consequence, standards have been promulgated including those in the Department of Defense document which is identified as DOD-STD-1399(NAVY) SECTION 300 1 AUG. 1978 and which is entitled MILITARY STANDARD INTERFACE STANDARD FOR SHIPBOARD SYSTEMS SECTION 300 ELECTRIC POWER, ALTERNATINC CURRENT. Of particular relevance is the following section.
(For a power-source frequency of 60 Hz, a 1 kVA or more unit rating is specified.)
In Table I. (on page 5) the total harmonic distortion is limited to 5 percent; and, in section 6.2.2 the power factor is limited to the range of 0.8 lagging to 0.95 leading. Further, in Table I. (on page 5) the worst case frequency excursion from nominal frequency is listed as 51/2 percent.
Heretofore, great difficulty has been had in meeting the above-mentioned standard.
It has been suggested that a filter be used to "trap and shunt undesirable harmonics." To illustrate the the problems associated with the use of a filter to isolate from an AC power line, harmonic currents a DC power supply would, otherwise, generate on the line, performance characteristics were calculated for a circuit in which the above-mentioned (capacitor-input-type) DC power supply was coupled to the line by means of a filter designed to match a zero ohm source (driving) impedance to a 144 ohm load impedance. Specifically, an 8-pole, Butterworth, low pass filter was designed. (First, for low, pass band attenuation, 60 Hz was set equal to 0.7 omega, making omega equaled to 86 Hz. Next, it was noted that when the above-mentioned (capacitor-input-type) DC power supply was directly connected to the AC power line, the third harmonic level was approximately 94%. Also, it was noted that the above-mentioned military specification required that the third harmonic level not exceed 3%. Thus, an 8-pole filter (n equal 8) was chosen to provide an approximate 30:1 voltage reduction (approximately 50 dB) at 180 Hz (2.1 omega). Also chosen was a d of 0.02.
As a consequence for the 8-pole, Butterworth, low pass filter:
______________________________________ L(1) = 1.398 C(2) = 1.963 L(3) = 1.648 C(4) = 1.602 L(5) = 1.243 C(6) = 0.9613 L(7) = 0.5829 C(8) = 0.1982. ______________________________________
(Where L(1) is connected in series with the AC power line; and, C(8) is connected across the input of the DC power supply.) These component values were scaling for omega equal to two pi times 86 Hz. and Z(0) equal to 144 ohms. (L' equals 144 divided by the quantity of two pi times 86 Hz.; and, C' equals one divided by the quantity 144 times two pi times 86 Hz.) (See, for example, pages 7, 8, and 136 of the first edition (1963) of the book by Philip R. Geffe which is entitled Simplified Modern Filter Design.) As a consequence:
______________________________________ L(1) = 0.3726 H C(2) = 25.23 mfd L(3) = 0.4392 H C(4) = 20.59 mfd L(5) = 0.3312 H C(6) = 12.35 mfd L(7) = 0.1553 H C(8) = 2.547 mfd. ______________________________________
______________________________________ Harmonic currents generated on an AC power line by a DC power supply coupled to the line by the 8-pole, Butterworth, low pass filter level of the harmonic currents relative the fundamental ______________________________________ 1st 100.00% 2nd 0.22% 3rd 0.08% 4th 0.08% 5th 0.07% 6th 0.06% 7th 0.06% 8th 0.06% 9th 0.05% ______________________________________ Total Harmonic Load Power Frequency Output Level ______________________________________ 200 Ohms 50 W 60 Hz 100 V DC 0.4% ______________________________________
It is important to note the relatively low potential (100 volts) which was developed across the load, as compared to the 162 volt DC potential which was developed by the DC power supply across the 200 ohm (131 watt) load without the filter. In addition, the circuit exhibited a number of other, undesirable, characteristics. Noted was a 15 ms delay, a 32 ms overshoot, a resonant boost, a current lag, and an impulse in the output following the start impulse. Further, the phase angle of the fundamental would suggest a power factor of 0.66. Finally, it is important to note the size of the components.
The use of series-connected, parallel-resonant, inductor-capacitor-type "LC filters" is shown in three prior-art patents. The German patent DE 3012-747 of Wilhelm Kleische shows (in the sole figure) what is referred to (in the Abstract) as an "LC filter circuit". The "LC filter circuit" includes the parallel combination of an inductor (L) and a capacitor (C). The "LC filter circuit" is shown connected in series with the primary of a transformer (T) across an incoming main (an AC power line?). The secondary of the transformer (T) is shown connected across the input of a bridge rectifier of a (capacitor-input-type) DC power supply (C and Co). It is indicated that.
The Japanese patent 58[1983]-163271 of Kawaguchi Yuuji et al shows (in FIG. 1) what is referred to (in the Abstract) as a "filter circuit" (7). The "filter circuit"includes the parallel combination of an inductor (2) and a capacitor (3). The "filter circuit" (7) is shown connected to couple the input of a (capacitor-input-type) DC power supply (of an "inverter unit") (8) to a "commercial power supply" (AC power line?) (1). It is indicated (in the Abstract) that the "filter circuit" is
Further, it is indicated (in the body of the patent) that the "filter circuit" is resonant at the third harmonic. The Q was not specified. Finally, it is indicated (in the body of the patent) that
The Japanese patent 56[1981]-157261 of Kouichi Noguchi shows (in FIG. 3) what is referred to (in the Abstract) as an "overcurrent limiting capacitor" (10) and three "parallel resonant circuits" (16, 17, and 20). Each "parallel resonant circuit" includes the parallel combination of an inductor and a capacitor (the inductor of "circuit" 16 being designated 15 and the capacitor of the "circuit" being designated 14). The "overcurrent limiting capacitor" (10) and the three "parallel resonant circuits" (16, 17, and 20) are shown connected in series to couple the input of a (capacitor-input-type) DC power supply (which includes components 12, 11, and 13) to an "AC power source (9). As to the resonant frequency of the "circuits", it is indicated that
To illustrate the operation of series-connected, parallel-resonant "LC filters" of the type shown in the three, above-mentioned, prior-art patents, performance characteristics were calculated for a number of circuits. First, the performance characteristics were calculated for a circuit in which a (capacitor-input-type) DC power supply was directly connected (zero (0) "LC-filters") to an AC power line, as was previously discussed. Then, the performance characteristics were calculated for a circuit in which the DC power supply was coupled to the AC power line by means of a number of (series-connected, parallel-resonant) "LC filters." Calculations were performed for a circuit in which the DC power supply was coupled to the AC power line by means of one (1) (parallel-resonant) "LC filter", resonant at the third harmonic of the AC power line frequency. Next, calculations were performed for a circuit in which the DC power supply was coupled to the AC power line by means of two (2) (series-connected, parallel-resonant) "LC filters", resonant at the third and fifth harmonics of the AC power line frequency. Then, three (3) "LC filters" were used, resonant at the third, fifth, and seventh harmonics; four (4) "LC filters" were used, resonant at the third, fifth, seventh, and ninth harmonics; five (5) "LC filters" were used, resonant at the third, fifth, seventh, ninth, and eleventh harmonics; and, six (6) "LC filters" were used, resonant at the third, fifth, seventh, ninth, eleventh, and thirteenth harmonics. The "LC filters" had a Q of 1/2, as employed (below) in the present invention. Again, small resistors were included in series with various components to facilitate the calculations. A constant, 100 watt load was used, for reasons which will become apparent shortly. For the six (6) "LC filter" circuit, performance characteristics were calculated at various AC power line frequencies. At a frequency of 57 Hz, the DC potential developed across the load collapsed.
______________________________________ Harmonic currents generated on an AC power line by a DC power supply coupled to the line by a number of series- connected, parallel-resonant "LC filters" Number of Output "LC filters" Power Frequency Voltage Distortion ______________________________________ 0 131 W 60 Hz 162 V DC 157% 1 100 W 60 Hz 137 V DC 32% 2 100 W 60 Hz 130 V DC 15% 3 100 W 60 Hz 127 V DC 9% 4 100 W 60 Hz 121 V DC 6% 5 100 W 60 Hz 113 V DC 4.4% 6 100 W 60 Hz 102 V DC 3.1% 6 100 W 57 Hz * * 6 100 W 59 Hz 99 V DC 3.3% 6 100 W 61 Hz 107 V DC 3.8% 6 100 W 62 Hz 112 V DC 5.8% 6 100 W 63 Hz 119 V DC 9.3% ______________________________________
It is important to note the relatively low DC potential which was developed across the load, as compared to the 162 volt DC potential which was developed by the DC power supply across the load without the "LC filters". Also, it is important to note the sensitivity of the DC load potential to frequency.
The above-mentioned, series-connected, parallel-resonant "LC filters" form a simple series (loop) circuit with the generator of the AC power line and the input (of the bridge rectifier) of the DC power supply. As a consequence, the waveform of the current flowing through the input (of the bridge rectifier) of the DC power supply must be the same as the waveform of the current flowing through the generator of the AC power line. From the sinusoidal voltage waveform developed across the AC power line, the "LC filters" develop across the input (of the bridge rectifier) of the DC power supply a trapezoidal (near square-wave) voltage waveform having a peak level, which is just slightly greater that the level developed at the output of the DC power supply.
Disclosed in the British patent 1,472,411 of T. Kennedy is a filter network which is for use with a load having a non-linear control device (saturable reactor) and which is for absorbing unwanted harmonic currents. The filter network employs a plurality of filters each including an inductor and a capacitor which is connected in series with the (associated) inductor. Each of the filters (inductor-capacitor combinations) is connected in parallel with the load. An additional inductor is employed connected between the AC power line and the load to couple the load to the AC power line. It is indicated (on page 2 in lines 113-115 of the T. Kennedy patent) that each of the filters (inductor-capacitor combinations) is tuned to a frequency less than the harmonic frequency which it is to filter. Further, it is indicated (on page 3 in lines 115-128) that
In an example in the T. Kennedy patent it is indicated (on page 4 in lines 109-112) that 70 percent of the harmonic currents are removed and 30 percent of the harmonic currents are reflected into the AC power line. Further, it is indicated (on page 4 in lines 112-115) that
Although of some value in reducing the level of some of the harmonic currents, it is important to note that the reductions in the levels of harmonic currents afforded by the network disclosed in the above-mentioned T. Kennedy patent does not approach that required to meet the above mentioned standard.
In the U.S. Pat. No. 4,222,096 of D. Capewell and the U.S. Pat. No. 4,369,490 of F. Blum a circuit is disclosed which includes a capacitor connected in parallel with the input of the bridge rectifier of a (capacitor-input-type) DC power supply and an inductor connected between the AC power line and the input of the rectifier to couple the DC power supply to the AC power line. In the F. Blum patent it is indicated (on column 5 in lines 23-29) that without the above-mentioned circuit, the DC power supply was found to present a power factor of 65 percent to the AC power line. Also, it was found that without the above-mentioned circuit, the level of the third harmonic current was 88 percent, the level of the fifth harmonic current was 65 percent, and the level of the seventh harmonic current was 38 percent of the level of the fundamental current. In one example, With the above-mentioned circuit, the DC power supply was found to present a power factor of 94 percent to the AC power line. Also, with the above-mentioned circuit, the level of the third harmonic current was 20 percent, the level of the fifth harmonic current was 6 percent, and the level of the seventh harmonic current was 2 percent of the level of the fundamental current.
Although the above-mentioned circuit greatly increases the power factor a DC power supply presents to an AC power line and greatly reduces the levels of the harmonic currents, It is important to note that the DC power supply (and circuit combination) still does not even come close to meeting the above-mentioned military standard.
The U.S. Pat. No. 3,461,372 of Clive Pickup et al. shows (in the sole figure) what is referred to in the Patent as a "D.C. to A.C. power converter". Shown is a switching transistor (3) configured to alternately switch on and off power from a DC source (Vc) responsive to a square wave (1-2), a plurality of series resonant "circuits" (4-5, 6-7, and 8-9) configured to "attenuate" lower even harmonics, and a plurality of parallel resonant "circuits" (10-11, 12-13, and 14-15) configured to "block" odd harmonics, the combination to provide a sinusoidal output across a load (R1). More specifically, the collector of the transistor (3) is coupled to the D.C. source (Vc) by an inductance (Lf). Further, the plurality of series resonant "circuits" (4-5, 6-7, and 8-9) are each connected between the collector and the emitter of the transistor (3). Finally, the plurality of parallel resonant "circuits" (10-11, 12-13, and 14-15) are connected between the collector and the output. It is indicated (in column 2, lines 39-41) that the plurality of series resonant "circuits" (4-5, 6-7, and 8-9) are each tuned to a different even harmonic (2f. 4f. and 6f being shown in the figure). Further, it is indicated (in column 2, lines 41-44) that the inductance (Lf) is parallel resonant at the driving frequency with the effective capacitance of all the series resonant "circuits" (4-5, 6-7, and 8-9). Finally, it is indicated (in column 2, lines 44-47) that the parallel resonant "circuits" are resonant at the odd order harmonics (3f, 5f, and 7f being shown in the figure). It is important to note that the C. Pickup, et al Patent does not pertain to D.C. power supplies nor power factor, let alone the power factor a D.C. power supply presents to an AC power line.
Performance characteristics were calculated for a circuit in which a (capacitor-input-type) DC power supply was coupled to an AC power line by means of three parallel-resonant series-connected inductor-capacitor-type "circuits", which were, respectively, resonant at the third, the fifth, and the seventh harmonic frequencies of the AC power line frequency. In addition, three series-resonant shunt-connected inductor-capacitor-type "circuits" were connected across the AC power line, which were, respectively, resonant at the second, the fourth, and the sixth harmonic frequencies of the AC power line frequency. Finally, connected across the AC power line, was an inductor, having an inductance chosen to parallel resonant at the power line frequency with the effective capacitance of all the series resonant "circuits". The three parallel-resonant series-connect inductor-capacitor-type "circuits" had a Q of 1/2; and, the three series-resonant shunt-connected inductor-capacitor-type "circuits" had a Q of one, as employed (below) in the present invention. A sine wave AC power line potential; and, a 144 ohm load were used. Again, as previously indicated, small resistors were included in series with various components to facilitate the calculations. The total harmonic distortion was reduced to 15.6%. However, it is important to note the DC power supply only developed a DC potential of 122 volts across the load, as compared to the 162 volt DC potential which was developed by the DC power supply across the 200 ohm (131 watt) load when directly connected across the AC power line.
Next, the performance characteristics were calculated for a circuit in which the DC power supply was coupled to the AC power line by means of a network which includes various parallel-resonant series-connected inductor-capacitor-type "circuits" and various series-resonant shunt-connected inductor-capacitor-type "circuits". The "circuits" were all resonant at odd harmonic frequencies of the AC power line frequency (third, fifth, seventh, etc.).
__________________________________________________________________________ Harmonic currents generated on an AC power line by a DC power supply coupled to the line by a number of series- connected parallel-resonant "circuits", a number of series- resonant "circuits" being connected across the AC power line. # of # of series parallel resonant resonant Output circuits circuits Load Power Freq. Voltage Dist. __________________________________________________________________________ 0 0 200 Ohms 131 W 60 Hz 162 V DC 157% 1 1 200 Ohms 97 W 60 Hz 139 V DC 47% 1 1 100 W 100 W 60 Hz 138 V DC 49% 2 2 200 Ohms 87 W 60 Hz 132 V DC 43% 2 2 100 W 100 W 60 Hz 131 V DC 39% 3 3 200 Ohms 85 W 60 Hz 130 V DC 44% 3 3 100 W 100 W 60 Hz 127 V DC 40% 4 4 200 Ohms 81 W 60 Hz 127 V DC 46% 4 4 100 W 100 W 60 Hz 120 V DC 43% 5 5 200 Ohms 77 W 60 Hz 124 V DC 47% 5 5 100 W 100 W 60 Hz 103 V DC 45% 6 6 200 Ohms 73 W 60 Hz 121 V DC 48% 6 6 100 W 100 W 60 Hz 103 V DC 48% __________________________________________________________________________
Again, it is important to note the relatively low DC potential which was developed across the load, as compared to the 162 volt DC potential which was developed by the DC power supply across the 200 ohm (131 watt) load when directly connected across the AC power line (zero (0) "LC-filters"). Further, it is important to note the relatively poor regulation provided. Also, it is interesting to note that the level of certain harmonics increased as additional "circuits" were added.
The German patent (Offenlegungsschrift, 1,927,415, Jan. 2, 1979) of Hemesh Laxmidas Thanawala dated Jan. 2, 1970, "concerns an arrangement for high-voltage direct-current-transmission by connecting an alternating-current-network with a direct-current-network over a static frequency-changer and a transformer." Apparently, the object of the invention is to provide a "filter" permitting the reduction of the leakage inductance (and, thus, the size) of the transformer and the size of the thyratron tubes. shown in block form are (just) two basic topologies. However, each block is to be replaced by one, or more, networks chosen from thirteen basic resistor-capacitor-inductor networks, which are, also, shown.
More specifically, FIGS. 1a, 1b, and 2 are similar, FIGS. 1a and 1b taking an abstract form and FIG. 2 taking a combined schematic and block form. Each of these figures (FIGS. 1a, 1b, and 2) shows the combination of a three-phase network (1), a transformer (2), and a static rectifier (3), which is coupled to the network by the transformer. In addition, FIGS. 1a and 1b show a block labeled "F" (4); and, FIG. 2 show three blocks, which are respectively labeled "Fa", "Fb", and "Fc". In FIG. 1a, the block labeled "F" (4) is shown connected between the three-phase network (1) and a point "E", having earth potential; and, in FIG. 1b, the block labeled "F" (4) is shown connected between the transformer (2) and point "E". In FIG. 2, each of the blocks ("Fa", "Fb", and "Fc") is shown connected between a respective line of the three-phase network and point "E". In other words, the block(s) are connected in a simple "shunt" configuration. The blocks labeled "F" (4) and "Fa", "Fb", and "Fc" are referred to as "parallelfilters".
FIGS. 6 and 7 of the Thanawala patent are similar, FIG. 6 taking an abstract form and FIG. 7 taking a combined schematic and block form. Again, FIGS. 6 and 7 each shows the combination of a three-phase network (1), a transformer (2), and a static rectifier (3), which is connected to the transformer. However, FIGS. 6 shows three blocks, which are respectively labeled "F3", "F2", and "F1". The three blocks ("F3", "F2", and "F1") are connected in a "pi" configuration. Specifically, the block labeled "F3" is connected between the three-phase network (1) and the transformer (2). The block labeled "F2" is connected between the three-phase network (1) and point "E"; and, block labeled "F1" is connected between the transformer (2) and point "E". FIGS. 7 shows three sets of three blocks, which are, again, respectively, labeled "F3", "F2", and "F1". Each set of three blocks ("F3", "F2", and "F1") is connected in the "pi" configuration, one set for each line of the three-phase network (1). The blocks labeled "F3" are referred to both as "rejector-circuits" and as "filters"; and, the blocks labeled "F2" and "F1" are, again, referred to as "parallelfilters".
For use in the "filter" blocks, the Thanawala patent shows thirteen basic resistor-capacitor-inductor sub-networks. Shown in FIG. 3a of the Thanawala patent is the series combination of a capacitor, an inductor and a resistor; the series combination of a capacitor and a resistor is shown in FIG. 3b; a capacitor connected in series with an inductor, which is connected in parallel with a resistor, is shown in FIG. 3c; in FIG. 3d a capacitor is shown connected in series with an inductor, which is connected in parallel with the series combination of another capacitor and a resistor; and just a single capacitor is shown in FIG. 3e. In FIG. 5a of the Thanawala patent is shown the parallel combination of a capacitor, an inductor and a resistor; the parallel combination of a capacitor and a resistor is shown in FIG. 5b; a capacitor connected in series with a resistor, which is connected in parallel with an inductor, is shown in FIG. 5c; in FIG. 5d an inductor is shown connected in parallel with the series combination of a capacitor and the parallel combination of an inductor and a resistor; and just a single inductor is shown in FIG. 5e. FIG. 9a shows the series combination of an inductor and a capacitor, the combination connected in parallel with the series combination of another capacitor and a resistor. In FIG. 9b a capacitor is shown connected in series with an inductor, which is connected in parallel with the series combination of another capacitor and a resistor. Finally, in FIG. 9c, a capacitor is shown connected in parallel with a block.
In the translation, it is indicated that the "filter" block sub-networks (shown in FIGS. 3a-3e, 5a-5e, and 9a-9c of the Thanawala patent) are tuned to the "harmonics one wants to suppress" (page 3, line 2, of the translation). Further, it is indicated that the "F1" block is for "drawing away the harmonics from point C . . . to earth" (page 2, line 37, of the translation); that the "F2" block is for "drawing away the harmonics from point C . . . to earth" (page 2, line 38, of the translation); and, that the "F3" block is for "suppressing undesirable harmonics" (page 2, line 52, to page 3, line 1, of the translation). As an example, it is indicated (page 2, lines 43-50, of the translation) that the three sub-networks (parallel branches) shown in FIG. 4 can be tuned to the 5th, 7th, and 11th "or a higher harmonic". In other words, the "filter" block sub-networks are tuned to the ODD harmonics, including the the "filter" block sub-networks shown in FIGS. 3a-3e.
It is important to note how many different configuration are encompassed by the Thanawala patent. Considering only one phase of the three phases of the structure shown in block form in FIG. 7 (of the Thanawala patent) and considering only the choices shown in FIGS. 3a-3e, 5a-5e and 9a-9c, "F1" can have at least three sub-networks (as shown in FIG. 4) each chosen from one of the five choices shown in FIGS. 3a-3e; "F2" can have at least one sub-network chosen from the five choices shown in FIGS. 3a-3e; and, "F3" can have at least two sub-networks (as shown in FIG. 8) each chosen from one of the eight choices shown in FIGS. 5a-5e and 9a-9c. In other words, there are, approximately, (5)(5)(4)(5)(8)(8) or (32,00) choices for one phase of FIG. 7 alone. In addition, each of these sub-networks can be tuned to different harmonics. Considering only the 3rd, 5th, 7th, 9th, 11th, and 13th harmonics, there are six choices for each sub-network, (5)(6)(5)(6)(4)(6)(5)(6)(8)(6)(8)(6) or (1,492,992,000) choices. Further, each of these sub-networks can have a different Q.
Further, it is important to note that Thanawala considers the various blocks to be "filters"; and, thus, teaches that filter considerations should be employed in selecting, tuning and choosing the Q of the various sub-networks (shown in FIGS. 3a-3e, 5a-5e, and 9a-9c of the patent).
In a more modern system, the "pi" filter of the Thanawala patent is problematic in that "filter" block "F2" is connected directly across the AC power line. As connected, this "filter" block presents a low impedance to harmonics generated elsewhere in the AC power system. Consequently, the "filter" block is subject to overload.
For purposes herein, it is important to note that none of the topologies shown in the Thanawala patent (neither the simple shunt topology shown in FIGS. 1a, 1b, and 2, nor the "pi" topology shown in FIGS. 6 and 7) are the same as any of the topologies of the present invention. Further, none of the sub-networks of FIGS. 3a-3e, or any of the other figures shows a simple series connected inductor-capacitor network, as employed in the "resonators" of the present invention. Further, none of the sub-networks of FIGS. 5a-5e, or any of the other figures shows a simple parallel connected inductor-capacitor network, as employed in the principal "reflectors" of the present invention.
The reader may also find of interest, the U.S. Pat. No. 2,138,996 of Alan D. Blumlein; the U.S. Pat. No. 2;008,515 of Walter Plathner et al; the U.S. Pat. No. 4,591,963 of Daniel D. Retotar; the British patent 221,850 of Ernest Y. Robinson; the German patent 659,504; the article entitled "Filter Design Simplified" by Berthold Sheffield from Audio Engineering Vol. 35, No. 5, pages 26, 28, and 58; and the article entitled "Computer-Aided, Lumped-Element Filter Design and Analysis" by A. Kwon from Microwave Journal March 1976, pages 53, 54, and 57.